Due to the limited reserves of fossil fuels and worries about emission of greenhouse gases there is an increasing focus on using renewable energy sources.
Plant material comprising lignocellulose-containing material can be converted into fermentable sugars and used as an energy source by fermenting organisms including bacteria, yeast and fungi for industrial purposes. For example, Lignocellulose-containing material can be converted into sugars by enzymes, and the resulting sugars can be used as a feedstock for industrial microorganisms to produce products such as plastics and ethanol.
Production of fermentation products, such as ethanol, from fermentation of lignocellulose-containing material is known in the art and conventionally includes pretreatment, hydrolysis, and fermentation of the lignocellulose-containing material.
Pre-treatment lignocellulose-containing material results in the release of, e.g., acetic acid, phenolics and furans, from the lignocellulose-containing material that may irreversibly bind enzymes added during hydrolysis and fermentation. These compounds may also be toxic to the fermenting organism's metabolism and inhibit the performance of the fermenting organism. To overcome this inhibition of yeast it has been practised to dilute the hydrolyzate and ferment at a low dry solids concentration thereby achieving a corresponding dilution of the concentration of the inhibitory compounds.
It is also well known that by increasing the pH the toxicity of especially the acetic acid and other weak acids to the yeast can be reduced. However, in order to control contamination by spoilage bacteria the fermentation of hydrolysed lignocellulose-containing material is generally performed at acid pH (below 5.5). Thus, fermentation of hydrolysed lignocellulose-containing material is usually performed at a low pH and in low dry solids concentrations.
There is a need for improved processes for production of fermentation products from lignocellulose-containing material.